The present invention pertains to a process for gas phase removal of contaminants such as oxides, organics and metals from the surface of a substrate.
The removal of contamination from a substrate is an important step in the semiconductor fabrication process. Trace metals and other contaminants can cause degradation of device performance if not removed from the substrate surface. Contamination, whether in the form of oxide, organics or metals, can arise from a number of sources including wet chemicals, photoresist, ion implantation and redeposition of sputtered materials from chamber surfaces during plasma processing.
Many different etching and cleaning techniques have been developed for various semiconductor processes. Typically in the past, wet etches, such as xe2x80x9cRCA Cleanxe2x80x9d, dominated in semiconductor fabrication processes. Gradually, as device structures have shrunk and the move toward VLSI devices grown, dry etches have gained prominence. These dry etches include plasma and gas-based etches and many were developed originally for removing oxides and carbon-based contaminants.
For dry gas-phase metal removal, for example, several systems have been reported. U.S. Pat. Nos. 5,094,701 and 5,221,366 disclose use of beta-diketone and beta-ketoimine ligand forming compounds, which are dispersed in an oxidizing atmosphere. At a sufficient temperature, volatile metal-ligand complexes are reported to be formed and then sublimed from the surface. Temperatures of 200xc2x0 C. to 300xc2x0 C. are indicated to be required. U.S. Pat. Nos. 5,213,621, 5,213,622, and 5,332,444 disclose other ligand forming chemical reagents which reportedly can be used in a similar manner to form volatile metal-ligand complexes with surface impurities which then can be sublimed from the surface.
Other dry gas-phase removal techniques involve the use of ultraviolet radiation to generate cleaning radicals. Sugino et al. (IEIC Trans. Electron. Vol. E75-C, No. 7, July 1992) describe a system for removal of Fe and Al on a silicon surface using photoexcited chlorine radicals at approximately 20 Torr and 170xc2x0 C. as a cleaning gas. U.S. Pat. No. 5,221,423 issued to Sugino discloses a method for removing Al, Fe, Na and Cr by irradiating chlorine gas at a partial chlorine pressure of 20 Torr to produce chlorine radicals. U.S. Pat. No. 5,178,721 issued to Sugino discloses a Uv radical generating cleaning method in which the pressure of the chlorine gas and the pathlength of the UV are varied to maximize radical generation and cleaning efficiency. In that system, the chlorine pressure ranges from 1 Torr to atmospheric pressure. Ito (Proc. Instit. for Environ. Studies 1991 p.808) discloses a method for cleaning using photoexcited chlorine radicals wherein the chlorine is delivered at a pressure of 20 Torr.
Commonly assigned U.S. Pat. No. 5,954,884 discloses a chlorine based dry-cleaning system appropriate for removing metal contaminants from the surface of substrate in which the metal contaminant is chlorinated and reduced to a volatile metal chloride by UV irradiation.
Along with the advances in process design, advances have been made in equipment design to facilitate efficient implementation of the ever-more complex treatment processes. To that end, commonly assigned U.S. application Ser. No. 08/955355 discloses an apparatus which provides for the dual use of a UV source to heat a substrate and to facilitate photochemistry necessary for the treatment of the substrate.
There continues, however, to be a need for improved processes for removal of contaminants from substrates such as semiconductor substrates and substrates in micromechanical devices and the like. This need is amplified by the increasingly stringent performance criteria associated with the continuing drive toward miniaturization of semiconductors.
All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
The present invention is directed in one embodiment toward a gas phase process of removing contaminants from a semiconductor substrate without roughening the substrate. The method comprises the steps of irradiating the substrate in the absence of a halogen-containing gas followed by exposing the substrate to a halogen-containing gas in the absence of ultraviolet radiation. In another embodiment, the invention is directed toward a method of treating a semiconductor substrate to remove contaminants such as silicon oxides, organic and metallics from the surface of the substrate without excessive surface roughening and without destroying desirable features on the surface of the substrate such as shallow trench isolation. The method comprises the steps of heating the substrate via the application of ultraviolet radiation in the absence of a halogen-containing gas followed by exposing the heated substrate to a halogen-containing gas in the absence of ultraviolet radiation.
In yet another embodiment the invention is directed to a method of treating a substrate comprising the steps of performing an oxide etch, heating the substrate via the application of ultraviolet radiation in the absence of a halogen-containing gas, exposing the heated substrate to a halogen-containing gas in the absence of ultraviolet radiation and subsequently oxidizing the substrate.